Method and apparatus for packaging a microelectronic die

ABSTRACT

The present invention is directed toward methods and apparatuses for encapsulating a microelectronic die or another type of microelectronic device. One aspect of the present invention is directed toward packaging a microelectronic die that is attached to either a first surface or a second surface of a substrate. The die can be encapsulated by positioning the die in a cavity of a substrate and sealing the substrate to the substrate. The method can further include injecting an encapsulation compound into the cavity at a first end of the substrate to move along the first surface of the substrate. This portion of the compound defines a first flow of compound along the first surface that moves in a first direction from a first end of the substrate toward a second end of the substrate. Several embodiments of the method also include driving a portion of the compound through the substrate at a pass-through location or a secondary gate that is spaced apart from the first end of the substrate to generate a second flow of compound along the second surface of the substrate. The second flow of compound moves in a second direction toward the first end of the substrate. As the first and second flows of compound move through the mold, the method includes inhibiting a third flow of compound from moving in the first direction along the second surface of the substrate between the first end of the substrate and the pass-through location.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of pending U.S. patent application Ser.No. 09/595,623, filed on Jun. 16, 2000.

TECHNICAL FIELD

This invention relates to methods and apparatuses for packagingmicroelectronic devices; more particularly, this invention relates toencapsulating microelectronic dies in the manufacturing of memorydevices, microprocessors and other types of microelectronic devices.

BACKGROUND OF THE INVENTION

Many packaged microelectronic devices have a substrate, amicroelectronic die attached to the substrate, and a protective coveringencasing the die. The protective covering is generally a plastic orceramic compound that can be molded to form a casing over the die. Themicroelectronic die can be a memory device, a microprocessor, or anothertype of microelectronic assembly having integrated circuitry. Severaltypes of packaged devices also include bond pads on the substrate thatare coupled to the integrated circuitry of the die. The bond pads mayalternatively be coupled to pins or other types of terminals that areexposed on the exterior of the microelectronic device for connecting thedie to buses, circuits and/or other microelectronic assemblies.

A significant limiting factor for manufacturing packaged microelectronicdevices is encapsulating the die with the protective covering. The diesare sensitive components that should be protected from physical contactand environmental conditions to avoid damaging the die. The protectivecasing encapsulating the die, therefore, should seal the die from theenvironmental factors (e.g., moisture) and shield the die fromelectrical and mechanical shocks.

One conventional technique for encapsulating the die is known as“transfer-molding,” which involves placing the die and at least aportion of the substrate in a cavity of a mold and then injecting athermosetting material into the cavity. The thermosetting material flowsover the die on one side of the substrate until it fills the cavity, andthen the thermosetting material is cured so that it hardens into asuitable protective casing for protecting the die. The protective casingshould not have any voids over the die because contaminants from themolding process or environmental factors could damage the die. Thethermosetting material, moreover, should not cover a ball-pad array onthe substrate or damage any electrical connections between the die andthe substrate. Therefore, it is important to control the flow of thethermosetting material in the cavity to avoid (a) producing voids in theprotective casing over the die, (b) covering portions of the substratewith the thermosetting material that are not to be covered with theprotective covering, and (c) displacing or otherwise damaging any wiringor solder joints between the die and the substrate.

One drawback of transfer-molding is that it is difficult to avoidproducing voids in the thermosetting material. In one particulartransfer-molding technique, a first protective casing is formed over thedie on a first surface of the substrate, and a second protective casingis formed over contacts on the die and wire-bond connections on a secondsurface of the substrate. The first casing is formed from a first flowof the thermosetting compound, and the second casing is formed from asecond flow of the thermosetting compound. This transfer-moldingtechnique may result in voids along either the first or second surfaceof the substrate because the first and second flows may counter oneanother as they flow through the mold. Other transfer-molding techniquesmay also produce voids in the protective casing over the die because theflow of the thermosetting material in the mold may produce a first flowsection that moves in a direction counter to a second flow section.Therefore, it would be desirable to eliminate voids in the protectivecasing.

SUMMARY OF THE INVENTION

The present invention is directed toward methods and apparatuses forencapsulating a microelectronic die or another type of microelectronicdevice. One aspect of the present invention is directed toward packaginga microelectronic die that is attached to either a first surface or asecond surface of a substrate. The die can be encapsulated bypositioning the die in a cavity of a mold and sealing the substrate tothe mold. The method can further include injecting an encapsulationcompound into the cavity at a first end of the substrate so that thecompound moves along the first surface of the substrate. This portion ofthe compound defines a first flow of compound along the first surfacethat moves in a first direction from a first end of the mold toward asecond end of the mold. The method can also include driving a portion ofthe compound through the substrate at a pass-through location or asecondary gate that is spaced apart from the first end of the substrateto generate a second flow of compound along the second surface of thesubstrate. The second flow of compound moves in a second directiontoward the first end of the mold. As the first and second flows ofcompound move through the mold, the method includes inhibiting a thirdflow of compound from moving in the first direction along the secondsurface of the substrate between the first end of the substrate and thepass-through location.

Another aspect of this invention is a microelectronic device comprisinga substrate, a microelectronic die attached to substrate, and a coverencasing at least a portion of the die. The substrate can have a firstsurface, a second surface, and plurality of ball-pads on the secondsurface. The microelectronic die can have a first side attached to thefirst surface of the substrate, a plurality of contacts on the firstside, and an integrated circuit coupled to the contacts. The contacts ofthe die can be electrically coupled to the ball-pads of the substrate bya plurality of connectors. The cover can further include a first casingencapsulating the die and a portion of the first surface of thesubstrate, and a second casing encapsulating the contacts on the firstside of the die and the connectors. The first casing has a first end, asecond end, a first gate section at the first end, and a second gatesection also at the first end. The first and second gate sections arespaced apart from one another along the first end.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top cutaway isometric view of a microelectronic devicebefore being packaged in accordance with a method of one embodiment ofthe invention.

FIG. 2 is a side elevation view of the microelectronic device of FIG. 1.

FIG. 3A is a top plan view of a first mold section for encapsulating amicroelectronic device in accordance with an embodiment of theinvention.

FIG. 3B is a bottom plan view of a second mold section for use with thefirst mold section of FIG. 3A.

FIG. 4 is a partial front cross-sectional view of the first and secondmold sections of FIGS. 3A and 3B in an operating position in accordancewith an embodiment of the invention.

FIG. 5A is a partial front cross-sectional view of a microelectronicdevice being packaged using the first and second mold sections of FIG. 4according to an embodiment of the invention.

FIG. 5B is a side cross-sectional view of the microelectronic device ofFIG. 5A being packaged using the first and second mold sections of FIG.4 in accordance with an embodiment of the invention.

FIG. 6 is a top isometric view of a packaged microelectronic devicebefore singulation in accordance with an embodiment of the invention.

FIG. 7 is a bottom isometric view of a packaged microelectronic devicein accordance with an embodiment of the invention.

DETAILED DESCRIPTION

The following disclosure is directed toward packaged microelectronicdevices, and to methods for encapsulating a microelectronic die oranother type of microelectronic device. Several embodiments of theinvention are described with respect to memory devices, but the methodsand apparatuses are also applicable to microprocessors and other typesof devices. One skilled in the art will accordingly understand that thepresent invention may have additional embodiments, or that the inventionmay be practiced without several of the details described below.

FIG. 1 is a top cutaway isometric view of a microelectronic device 10that is to be encapsulated using a method in accordance with oneembodiment of the invention. The microelectronic device 10 can include asubstrate 20 and a microelectronic die 40 attached to the substrate 20by an adhesive 60. The microelectronic device 10 shown in FIG. 1illustrates the substrate 20 and the die 40 before encapsulating the die40 with an encapsulation compound, such as a mold compound. Thefollowing description is directed toward encapsulating a microelectronicdie on a flexible substrate, but it is expected that several embodimentsof methods and molds in accordance with the present invention may beused to encapsulate a large variety of electrical and/or non-electricalarticles. Therefore, the following description with respect toencapsulating the microelectronic die 10 shown in FIGS. 1-6 is forpurposes of illustration only, and is not intended to limit the scope ofthe invention.

The embodiment of the substrate 20 shown in FIG. 1 can have a first end21, a second end 22 opposite the first end 21, a first surface 23, and asecond surface 24 opposite the first surface 23. The substrate 20 canalso include an elongated slot 25 between the first and second surfaces23 and 24 that extends lengthwise along a medial portion of thesubstrate 20. Additionally, an aperture 26 can extend through thesubstrate 20 at secondary gate location or a pass-through location thatis generally proximate to the second end 22 of the substrate 20. Thesubstrate 20 is generally an interposing device that provides an arrayof ball-pads for coupling very small contacts on the microelectronic dieto another type of device. In the embodiment shown in FIG. 1, thesubstrate 20 includes a first array of ball-pads 27, a second array ofterminal pads 28 proximate to the slot 25, and a trace 29 or other typeof conductive line between each ball-pad 27 and corresponding terminalpad 28. The substrate 20 can be a flexible material or a substantiallyrigid material, and the traces 29 can be conductive lines that areprinted on the substrate in a manner similar to printed circuit boards.

The embodiment of the microelectronic die 40 shown in FIG. 1 includes afirst side 41 attached to the first surface 23 of the substrate 20 bythe adhesive 60. The microelectronic die 40 can also include a pluralityof small contacts 42 and an integrated circuit 44 (shown schematically)coupled to the contacts 42. The contacts 42 are arranged in an arrayalong the first side 41 of the microelectronic die 40 so that thecontacts 42 are aligned with or otherwise accessible through the slot 25in the substrate 20. A plurality of wire-bonds or other types ofconnectors 50 couple the contacts 42 of the die 40 to correspondingterminal pads 28 on the substrate 20. As such, the substrate 20distributes the very small contacts 42 to the larger array of ball-pads27.

The adhesive 60 can be a two-sided tape or a decal adhered to the firstsurface 23 of the substrate 20 adjacent to the sides of the slot 25. Ina typical application, the adhesive 60 creates a small gap 61 at the endof the slot 25 toward the first end 21 of the substrate 20. The gap 61is defined by the distance between the first surface 23 of the substrate20 and the first side 41 of the die 40, which is generally equal to thethickness of the adhesive 60. As explained in more detail below, the gap61 can create several difficulties in encapsulating the terminal pads28, the connectors 50, and the contacts 42.

FIG. 2 is a side elevation view of the microelectronic device 10 afterthe die 40 and a portion of the substrate 20 have been encapsulated by amold compound 70. The mold compound 70 can be injected into a mold (notshown in FIG. 2) to form a first casing 72 that encapsulates the die 40and a second casing 74 that fills the slot 25 (FIG. 1). The first casing72 also covers a portion of the first surface 23 of the substrate 20,and the second casing 74 also covers the terminal pads 28 on thesubstrate 20 (FIG. 1), the connectors 50 (FIG. 1), and the contacts 42on the die 40 (FIG. 1).

The first casing 72 can be formed by injecting the mold compound througha gate of a mold at the first end 21 of the substrate 20 so that themold compound flows along the first surface 23 of the substrate 20 in afirst direction (shown by arrows A₁-A₃). The second casing 74 is thenformed by driving a portion of the mold compound through the aperture 26and/or another opening 62 defined by another gap at the other end of theslot 25 toward the second end 22 of the substrate 20. The aperture 26and/or the opening 62 define a pass-through location or a secondary gatelocation that is spaced apart from the first end 21 of the substrate 20to generate a second flow of compound along the second surface 24 of thesubstrate 20 (shown by arrows B₁-B₃). The second flow of mold compoundmoves in a second direction away from the second 22 end of the substrate20 toward the first end 21.

The process of fabricating the first and second casings 72 and 74 can bedifficult because a third flow of mold compound may pass through the gap61 between the die 40 and the substrate 20 at the end of the slot 25toward the first end 21 of the substrate 20 (arrow D₁). Such a thirdflow of mold compound would move counter to the second flow of moldcompound along the second surface 24 of the substrate 20. As a result,voids or other disparities may be created in the second casing 74 wherethe third flow of mold compound (arrow D₁) meets the second flow of moldcompound (arrows B₁-B₃). One aspect of the present invention is toinhibit creating the third flow of mold compound that moves in the firstdirection along the second surface 24 of the substrate 20 between thefirst end of the substrate 21 and the pass-through location toward thesecond end 22 of the substrate 20.

FIG. 3A is a top plan view of a first mold section 100 and FIG. 3B is abottom plan view of a second mold section 200 for forming the first andsecond casings 72 and 74 (FIG. 2) in a manner that inhibits oreliminates a third flow of mold compound through the gap 61 (FIG. 1)between the substrate 20 and the die 40. The embodiment of the firstmold section 100 shown in FIG. 3A includes a first end 102, a second end103, a bearing surface 120 for contacting the first side 23 of thesubstrate 20 (FIG. 1), and a first cavity 104 for receiving the die 40(FIG. 1). The cavity 104 can have a first side 105, a second side 106opposite the first side, a first end 107, and a second end 108 oppositethe first end. The first mold section 100 can also include a pluralityof gates including at least a first gate 110 a and a second gate 110 bthat are separated from one another by an island 112. The first gate 110a can open into the cavity 104 at a location proximate to the first side105, and the second gate 110 b can open into the cavity 104 at alocation proximate to the second side 106. The first and second gates110 a and 110 b can meet at a common feed port 114. The first and secondgates 110 a and 110 b define a gate pair that is coupled to a commonfirst cavity 104 in the first mold section. The first mold section 100can further include a flow restrictor 115 at the end of each of thefirst and second gates 110 a and 110 b. In operation, an injection flowF of molding compound or encapsulating compound is injected through thefeed port 114 and the gates 110 a and 110 b. The island 112 splits theinjection flow F into a first injection flow F₁ passing through thefirst gate 110 a and a second injection flow F₂ passing through thesecond gate 110 b.

FIG. 3B illustrates an embodiment of a second mold section 200 forforming the second casing 74 (FIG. 2) over the slot 25 of the substrate20 (FIG. 1). The second mold section 200 can include a bearing surface220 for contacting the second side 24 of the substrate 20 (FIG. 1). Thesecond mold section 200 can also include a second cavity 225 configuredto be superimposed over the slot 25 of the substrate 20 when the bearingsurface 220 engages the first surface 24 of the substrate 20.

FIG. 4 is a partial cross-sectional view of a mold assembly 400including the first mold section 100 shown in FIG. 3A and the secondmold section 200 shown in FIG. 3B. The first mold section 100 issuperimposed under the second mold section 200 so that the second cavity225 of the second encapsulating section is over the first cavity 104 ofthe first mold section 100. The island 112 positions the opening of thefirst gate 110 a toward the first side 105 of the first cavity 104 andthe opening of the second gate 110 b toward the second side 106 of thefirst cavity 104. Referring to FIGS. 3A and 4 together, the firstinjection flow F₁ flows through the first gate 110 a and enters thecavity 104 proximate to the first side 105, and a second injection flowF₂ flows through the second gate 110 b and enters the cavity 104proximate to the second side 106.

The first mold section 100 can have a plurality of individual firstcavities 104, and the second mold section 200 can have a plurality ofindividual second cavities 225. The first cavities 104 are arranged withrespect to the second cavities 225 so that each first cavity 104 issuperimposed under a corresponding second cavity 225. Additionally, thefirst mold section 100 can have a plurality of gate pairs that each havea first gate 110 a and a second gate 110 b. The openings of the firstand second gates 110 a and 110 b of each gate pair are spaced apart fromone another at the first end 107 of a corresponding first cavity 104. Assuch, the first mold section 100 can form a first casing 72 and a secondcasing 74 on a plurality of individual microelectronic devices in asingle molding cycle in a manner that provides a bifurcated flow of moldcompound into the first end of each of the first cavities 104.

FIGS. 5A and 5B illustrate an embodiment of a method for encapsulatingthe microelectronic die 40 and the slot 25 of the substrate 20. FIG. 5A,more specifically, is a partial front cross-sectional view illustratingthe microelectronic device 10 being encapsulated using the first andsecond mold sections 100 and 200. In this embodiment, the bearingsurface 120 of the first mold section 100 presses against a perimeterportion of the first surface 23 of the substrate 20, and the bearingsurface 220 of the second mold section 200 presses against the secondsurface 24 of the substrate 20. The bearing surface 220 of the secondmold section 200 can press against the second surface 24 of thesubstrate 20 by injecting a mold compound into the cavity 104, asexplained in U.S. patent application Ser. No. 09/255,554, which isherein incorporated by reference. The first and second injection flowsF₁ and F₂ of the mold compound pass through the first and second gates110 a and 110 b to enter the cavity 104 along the side regions of themicroelectronic die 40. As a result, the high pressure flow of moldcompound does not flow directly toward the gap 61 (FIG. 1) between thesubstrate 20 and the die 40 proximate to the first end 21 of thesubstrate 20. The first and second injection flows F₁ and F₂ of the moldcompound accordingly fill the first cavity 104 in a manner that does notcause the mold compound to generate a flow in the slot 25 of thesubstrate 20 that flows toward the second end 22 of the substrate 20.Therefore, the first and second gates 110 a and 110 b provide a moldthat inhibits voids or other asperities from forming in the secondcasing 74. Moreover, the first mold section 100 surprisingly does notcreate voids or asperities in the first casing 72 even though itproduces a bifurcated flow of mold compound in the first cavity 104.

FIG. 5B is a side cross-sectional view illustrating the flow of moldcompound through the first and second mold sections 100 and 200. Thefirst and second injection flows F₁ and F₂ of mold compound flow pastthe island 112 and into the first end 107 of the first cavity 104 tocreate a first flow A₁ heading in a first direction toward the secondend 22 of the substrate 20. The first flow A₁ of mold compound passesthrough the aperture 26 at the pass-through location toward the secondend 22 of the substrate 20 to generate a second flow B₁ of mold compoundthat flows through the second cavity 225 of the second mold section 200.The second flow B₁ of mold compound fills the slot 25 of the substrate20 and flows in a second direction until it reaches a terminal end 217of the second cavity 225.

FIG. 6 is a top isometric view of an encapsulated microelectronic device10 having the first casing 72 over the die 40 on the first surface 23 ofthe substrate 20. FIG. 6 illustrates the microelectronic device 10before it has been “singulated” to remove unnecessary portions of thesubstrate 20 and molding compound. In this embodiment, themicroelectronic die 40 (FIG. 1) and a portion of the substrate 20 areencapsulated by the first casing 72. Before singulating the device, themicroelectronic device 10 includes a flash section 80 of mold compoundhaving a first gate section 82 and second gate section 84. The firstgate section 82 corresponds to the portion of the mold compound in thefirst gate 110 a (FIG. 3A) at the end of the encapsulating process, andthe second gate section 84 corresponds to the portion of the moldcompound in the second gate 110 b.

FIG. 7 is a bottom isometric view of the microelectronic device 10having the second casing 74 over the slot 25 of the substrate 20. Inthis embodiment, the second casing 74 covers the terminal pads 28 (FIG.1), the connectors 50 (FIG. 1), and the contacts 42 on the first surface41 of the die 40 (FIG. 1). The microelectronic device 10 is thensingulated to remove the excess portion of the flash 80 and thesubstrate 20.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

What is claimed is:
 1. A method of encapsulating a microelectronicdevice having a substrate and a microelectronic die attached to a firstsurface of the substrate, the method comprising: positioning thesubstrate between a first mold section having a first cavity and asecond mold section having a second cavity, wherein the die is in one ofthe first or second cavities, and wherein a second surface of thesubstrate faces the other of the first or second cavities; injecting amold compound into the first cavity of the first mold section at a firstend of the substrate to create a first flow of mold compound movingthrough the first cavity toward a second end of the substrate; driving aportion of the first flow of mold compound through a secondary gatelocated toward the second end of the substrate to create a second flowof mold compound that moves through the second cavity toward the firstend of the substrate; and inhibiting a counter flow of mold compoundfrom moving through the second cavity from the first end of thesubstrate toward the second end of the substrate.
 2. The method of claim1 wherein inhibiting a counter flow of mold compound from moving throughthe second cavity comprises hindering the first flow of mold compoundfrom passing through the substrate at a location proximate to the firstend of the substrate.
 3. The method of claim 1 wherein: the first moldsection has a first gate at a first end of the first cavity and a secondgate also at the first end of the first cavity, the first and secondgates being spaced apart from one another; and inhibiting a counter flowcomprises preventing the first flow of mold compound from passingthrough the substrate at the first end of the substrate by injecting themold compound into the first cavity through the first and second gatesto bifurcate the first flow in the first cavity at the first end of thesubstrate.
 4. The method of claim 1 wherein: the substrate has a slotaligned with a contact array on the die; and inhibiting a counter flowcomprises preventing the first flow of mold compound from passingthrough a gap at an end of the slot proximate to the first end of thesubstrate by injecting the mold compound into the first cavity such thata flow path of the injected flow is not aligned with the slot in thesubstrate.
 5. A method of packaging an article, comprising: attaching amicroelectronic die to one of a first surface or a second surface of asubstrate such that an array of contacts on the die is accessible fromthe other of the first or second surface of the substrate; coupling thecontacts of the die to corresponding terminal pads on the other of thefirst or second surface of the substrate; positioning the substratebetween a first mold section having a first cavity and a second moldsection having a second cavity, wherein the die is in one of the firstor second cavities, and wherein the second side of the substrate is inthe other of the first or second cavities; injecting a mold compoundinto the first cavity of the first mold section at a first end of thesubstrate to create a first flow of mold compound moving through thefirst cavity toward a second end of the substrate; driving a portion ofthe first flow of mold compound into the second cavity at a locationtoward the second end of the substrate to create a second flow of moldcompound that moves through the second cavity toward the first end ofthe substrate; and inhibiting a counter flow of mold compound frommoving through the second cavity from the first end of the substratetoward the second end of the substrate.
 6. The method of claim 5 whereininhibiting a counter flow of mold compound from moving through thesecond cavity comprises hindering the first flow of mold compound frompassing through the substrate at the first end of the substrate.
 7. Themethod of claim 6 wherein: the first mold section has a first gate at afirst end of the first cavity and a second gate also at the first end ofthe first cavity, the first and second gates being spaced apart from oneanother; and hindering the first flow of mold compound from passingthrough the substrate at the first end of the substrate comprisesinjecting the mold compound into the first cavity through the first andsecond gates to bifurcate the first flow in the first cavity at thefirst end of the substrate.